Answer:
-1/2
Explanation:
If you connected the dots here you would have a straight line. The average rate of change for a straight line is also known as the slope. Slope, by definition, is rise over run (although rise doesn't necessarily mean "up"; it could also mean down, as it does here). From one point to the next in our graph, we go down 1 unit (-1) and to the right 2 units (+2). Therefore, the slope of the line is -1/2.